This invention relates generally to the vapor deposition of thin films and more particularly to the semiconductor devices fabricated by employing techniques set forth in U.S. patent application Ser. No. 07/177,563, filed Mar. 4, 1988, and U.S. patent application Ser. No. 07/354,052, filed May 19, 1989, a divisional application of U.S. patent application Ser. No. 07/177,053, U.S. Pat. No. 4,962,057, which are incorporated herein by reference thereto. Specifically, the semiconductor devices and structures disclosed herein are fabricated employing in situ photo induced modifications to compound films of such devices and structures during epitaxial growth.
The two above mentioned applications relate to in situ techniques using a scanned laser beam across or exposure of radiation through a mask to a growth surface to either selectively growth enhance and/or selectively evaporation enhance regions of the growth surface to provide three dimensional nonplanar effects in the film or layer in situ either during growth of a layer or upon termination of layer growth but prior to growth of the next layer. The enhancement effect is photo induced as taught in the foregoing applications and, in particular, is patterned to produce such three dimensional features to conform to desired geometrical and/or stoichiometric features in a semiconductor device or structure. Due to these abilities of enhancement effects, it is possible to grow desired configurations in situ without need for any intermittent removal of the structure from the processing reactor prior to completion of epitaxial growth eliminating oxygen or air, solvent, and etchant contamination and providing a resultant morphology that is sculpturally smooth and atomically continuous at processed regions of epitaxially grown layers.
Techniques in MBE processing using thermal evaporation have been employed to provide a pattern in heterostructures. In one case, a plurality of GaAs quantum well layers separated by AlGaAs barrier layers were grown in MBE on a GaAs substrate mounted on a slotted susceptor so that a temperature differential is established across the supported substrate. In this manner, the thickness of the deposited GaAs and AlGaAs layers would be thinner over deposited regions on firm substrate having a 30.degree. C. to 50.degree. C. higher temperature gradient over substrate temperature compared to adjacent regions over susceptor recesses. See W. D. Goodhue et al, "Planar Quantum wells With Spatially Dependent thicknesses and Al Content", Journal of Vacuum Science and Technology B, Vol. 6(3), pp. 846-849, May/June 1988. It was recognized that for quantum well structures grown above 700.degree. C., the thickness of these alternating well/barrier layers decreases as the temperature increases.
In another case, represented by two examples, patterning is achieved by quasi-in situ thermal processing wherein thermal etching is employed to selectively remove GaAs. In one example, a n-GaAs layer over a p-AlGaAs layer is first, selectively, chemically etched in a particular region followed by thermal etching to remove the remaining thin GaAs left from chemical etching before proceeding with regrowth of the p-AlGaAs layer. This forms a buried reverse biased current confinement mechanism in a double heterostructure laser. H. Tanaka et al, Single-Longitudinal-Mode Self Aligned AlGa(As) Double-Heterostructure Lasers Fabricated by Molecular Beam Epitaxy", Japanese Journal of Applied Physics, Vol. 24, pp. L89-L90, 1985. In the other example, a GaAs/AlGaAs heterostructure partially masked by a metallic film is thermally etched in an anisotropic manner illustrating submicron capabilities for device fabrication. A. C. Warren et al, "Masked, Anisotropic Thermal Etching and Regrowth for In Situ Patterning of Compound Semiconductors", Applied Physics Letters, Vol. 51(22), pp. 1818-1820, Nov. 30, 1987. In both of these examples, an AlGaAs masking layer is recognized as an etch stop to provide for the desired geometric configuration in thermally etched GaAs, although it is also known that, given the proper desorption parameters, AlGaAs may also be thermally etched at higher temperatures and different attending ambient conditions visa vis GaAs.
However, none of these techniques employ photo induced evaporation as a technique in a film deposition system to incrementally reduce, on a minute scale, film thickness in patterned or selective locations at the growth surface either during or after film growth in situ, producing smooth sculptured surface morphology which is a principal objective of this invention.
Thus, it is an object of this invention to fabricate heterostructures and semiconductor devices with various selective optical and electrical properties, such as, heterostructure laser arrays with multiple wavelength emitters, index waveguiding features, nonabsorbing waveguide and window features, phase locked arrays, distributed feedback structures, semiconductor wires and field effect transistors, produced by the patternable negative growth process of U.S. Pat. No. 4,962,057 coupled with the patternable positive growth process of U.S. patent application Ser. No. 07/354,052 or coupled with conventional nonpatternable positive growth processes capable of producing in situ three dimensional crystal features during in situ epitaxial growth of such heterostructures and semiconductor devices.